290 H. E. JORDAN 



homogeneous or segmented. While structurally very like 

 mitochondria — on the basis of which, characters I previously so 

 interpreted them — I now feel compelled to give them a different 

 interpretation, and for the following reasons: 1) Identical fila- 

 ments appear in the cells of the hepatic cords (compare figs. 31 

 and 32) and those of the mesonephric tubules of these embryos. 

 These cells are functionally active in a secretory way, strength- 

 ening the presumption that the filaments in the yolk-sac ento- 

 derm also have secretory significance. 2) If these filaments 

 were really mitochondria, many other cells should show such 

 elements, for it is well established that mitochondria are practi- 

 cally universally present in embryonal cells. But no other cells, 

 besides those mentioned, contain similar filaments in these 

 embryos. It is quite unreasonable to suppose that the technic 

 should have preserved mitochondria only in selected types of 

 cells. The filaments in question most probably have nothing 

 directly to do with mitochondria. 3) The filaments are appar- 

 ently identical with the ergastoplasmic filaments described by 

 Bensley (1) for the parenchymal cells of the pancreas of the 

 adult guinea pig, readily distinguishable from mitochondria 

 demonstrable by appropriate technics. Similar filaments have 

 been described for other secretory cells, as for example, salivary 

 glands and kidney. 



On the basis of the above considerations the conclusion seems 

 unavoidable that these filaments in the yolk-sac entoderm are 

 of secretory significance. The manner in which they function 

 in the secretion process is uncertain, but there is some evidence 

 that they segment distally into granules. These filaments, then, 

 may be presecretion filaments. In the 25 mm. stages, filaments 

 are relatively less, and granules relatively more, abundant than 

 at the 10 mm. stage. 



Similar structures have been described in the human yolk- 

 sac of about this same stage [Jordan (10, 11, and 12) ; Branca (2)]. 

 Branca indeed interpreted them as 'functional protoplasm.' 

 I first designated them by the term 'mucinous masses,' since 

 they reacted to the specific stains for mucus. In my first study 

 (1907) I inclined to the belief that they were degeneration prod- 



